Conventionally, as this kind of gas monitoring apparatus, there are an apparatus including a flow rate measurement unit for outputting a signal in response to the gas rate passing through a gas meter placed in a gas supplying pipe line, an individual gas appliance flow rate computation unit for calculating a change flow rate of the gas rate passing through the gas meter according to the signal from the flow rate measurement unit and classifying into the gas rate for each individual gas appliance, a sensor unit for providing input signals other than the change flow rate, such as outdoor air temperature, calendar information, and use start time information, for example, and a composite computation unit for compounding the information provided from the individual gas appliance flow rate computation unit and the sensor unit and determining the used gas appliance (for example, refer to patent document 1) and an apparatus including a sound producing unit each being installed in the individual gas flow path of each gas appliance for producing a monitor sound at a predetermined frequency corresponding to the individual gas appliance in the strength responsive to the gas flow rate and a monitor unit for monitoring the use state of the individual gas appliance based on the monitor sound produced by each sound producing unit (for example, refer to patent document 2).
As an apparatus for limiting the continuous use time to prevent an accident caused by forgetting to turn off a gas appliance, etc., an apparatus for setting the continuous use time in response to the flow rate and shutting off gas when the continuous use time has elapsed is available (for example, patent document 3).    Patent document 1: Japanese Patent Laid-Open No. H03-236513A    Patent document 2: Japanese Patent Laid-Open No. H08-178195A    Patent document 3: Japanese Patent Laid-Open No. H07-44239A